1. Field of the Invention
The present invention relates to a printing apparatus having a cap for protecting the nozzle formation surface of a printhead, and a method of moving the cap apart from the printhead when the cap sticks to the printhead.
2. Description of the Related Art
A printing apparatus such as an inkjet printing apparatus has a capping device which caps a nozzle formed in a printhead to discharge ink, in order to prevent drying and evaporation of ink and nozzle clogging caused by the ink while the printing apparatus is OFF or idle.
For example, the capping device vertically moves the cap to put the cap on the ink discharge surface of the printhead and remove the cap from it. The cap is moved (cap opening/closing operation) using a motor as a driving source. There has conventionally been known a printing apparatus using a dedicated cap motor as the driving source. There has also been known a printing apparatus which does not have a cap motor, moves a carriage supporting a printhead by a carriage motor, and while moving the cap in synchronism with the carriage, vertically moving the cap along a guide shaft or the like to open/close the cap.
For example, when the printing apparatus is turned on or receives an instruction to execute cleaning, and then receives an instruction to open the cap, it tries to open the cap by driving the cap motor or carriage motor. However, if the printing apparatus has remained OFF or idle for a long time, the cap has stuck to the printhead and cannot be opened even by driving the carriage motor or cap motor. If the cap does not open, neither printing processing nor cleaning processing is performed. In addition, a large current flows through the carriage motor or cap motor owing to feedback control of the motor, and may damage the capping device.
To avoid the damage to the capping device, a technique of moving a cap stuck to a printhead apart from the printhead is disclosed (e.g., Japanese Patent Laid-Open No. 2004-090293). A printing apparatus disclosed in Japanese Patent Laid-Open No. 2004-090293 has a capping device which moves down a cap in synchronism with the carriage operation. An encoder arranged in the carriage monitors the driving amount of a carriage motor which operates the carriage in order to open the cap. Upon the lapse of a predetermined time, it is determined whether or not the driving amount has reached a predetermined value. If no driving amount has reached the predetermined value, it is determined that the cap sticks to the printhead. To move the cap apart from the printhead, the carriage is slightly moved for a predetermined time (slight reciprocation). Then, the carriage is moved again to try to open the cap. By repeating this operation, the cap moves apart from the printhead. By slightly moving the carriage, bubbles enter the joint surface between the cap and the printhead mounted on the carriage little by little, moving the cap apart from the printhead.
However, it takes a long time to open the cap when the above-described operation to slightly move the carriage, then move the carriage again, and try to open the cap is repeated.
Instantaneously when the cap moves apart from the printhead by slightly moving the carriage, as described above, the load for driving the carriage drops, and the carriage might bump against the inner wall of the printing apparatus. The carriage moving width is about the width of a printing medium of the maximum size used in the printing apparatus, and walls are formed on the two sides. If an output current to the carriage motor is large in slightly driving the carriage, instantaneously when the cap moves apart from the printhead, the carriage moves at high speed, bumps against the inner wall of the printing apparatus, and may damage the printing apparatus.